1. Field of the Invention
The present invention relates to a thin film deposition process based on chemical vapor deposition using, as raw materials, organic metals, for example, PZT ferroelectrics, PLZT ferroelectrics, BaSr ferroelectrics, Cu high-temperature superconductors, and compound semiconductors such as GaAs semiconductors; a device therefor; a FTIR gas analyzer (a gas analyzer based on Fourier transform infrared spectrometry) used in the thin film deposition process; and a mixed gas supplying device used in the thin film deposition process.
2. Description of the Prior Art
In recent years, thin film deposition processes based on MOCVD (metal-organic chemical vapor deposition) have been used as a method for forming PZT ferroelectric thin films such as a PZT [Pb(Zr, Ti)O3] thin film. The method for forming a PZT ferroelectric thin film, using the MOCVD, comprises the steps of sending inert gas such as argon gas as carrier gas into raw material vaporizers containing as source materials, for example, organic metal materials Pb(C11H19O2)2, Zr(t-OC4H9)4 and Ti(i-OC3H7)4, respectively, (which comprise Pb, Zr and Ti, respectively, which are the main constituent elements of the PZT ferroelectric thin film), so as to produce three organic metal gases which contain Pb, Zr and Ti, respectively; mixing these organic metal gases in a gas mixing chamber; adding oxygen gas as an oxidizer thereto so as to produce a mixed organic metal gas; supplying the mixed gas into a reaction chamber whose temperature is kept to an appropriate value; and growing a thin film originating from this organic metal mixed gas on the surface of a substrate (for example, Pt/SiO2/Si, or Pt/MgO) set up in the reaction chamber.
The composition of the PZT ferroelectric thin film formed by the MOCVD is required to be stoichiometric. The composition of thin films obtained by thin film deposition processes in the prior art is controlled as follows.
That is, the temperatures (heating temperature) of the raw material vaporizers are first set up for the respective organic metal materials, and the concentrations of the respective gases are examined from the vapor pressures of the respective organic metal materials at the set-up temperatures. The concentrations of the respective organic metal materials are decided so as to correspond to a stoichiometric composition. Thereafter, the temperatures of the raw material vaporizers are subjected to fine adjustment. In this state, the flow rates of the carrier gases for the respective organic metal materials are set up to a constant value, so as to produce three organic metal gases. In this way, a PZT ferroelectric thin film is formed on an appropriate substrate.
The composition of the PZT ferroelectric thin film is analyzed with an analyzer such as an energy dispersion type X-ray analyzer (EDX). On the basis of the results, the temperature of the raw material vaporizer containing the organic metal material comprising an insufficient element, and the flow rates of the respective carrier gases are again adjusted. A PZT ferroelectric thin film is again formed.
The composition of this thin film is analyzed in the same manner as above to check whether or not the thin film has a given stoichiometric composition. When the thin film does not have the given stoichiometric composition, the above-mentioned work is repeated.
As described above, in conventional thin film deposition processes, a thin film is formed and subsequently the composition of this thin film is analyzed. When the analyzed composition is not a given stoichiometric composition, the conditions for generating the organic metal gases are amended and the process is repeated. Therefore, a problem that a significant amount of time is required for obtaining a thin film having a given composition arises. By repeating the formation of a thin film, the organic metal materials are consumed and the evaporation amounts of the organic metal gases change so that the composition of the gases can be out of a desired stoichiometric composition. That is, a problem of reproducibility arises.
The above-mentioned problems also arise in not only processes for depositing a PZT ferroelectric thin film but also processes for depositing a thin film, for example, a PLZT ferroelectric thin film, a Cu high-temperature superconductor thin film, or a compound semiconductor thin film such as a GaAs semiconductor thin film, by chemical vapor growth using an organic metal as a raw material.